Recent developments in overrunning roller clutches by the assignee of the current invention have provided new designs that change or improve nearly every aspect of standard roller clutch operation. Roller clutch load and speed capabilities have been improved to match or exceed the capability of the more expensive and tolerance dependent sprag clutches. One of the ways that roller clutch load capacity has been increased is to use two rows of rollers. Two rollers side by side can provide the load capacity of a single roller that is twice as long, but without the tendency of a long single roller to overload in the center if it skews. In U.S. Pat. No. 4,664,237 Lederman et al, a roller clutch is disclosed in which a single cage contains multiple pairs of rollers, side by side. Each roller pair is located in a single cage pocket, along with a special two sided spring that energizes each roller independently. Thus, each roller can move freely to its own ready position on the common cam ramp. The ready position of each roller, that is, its position on the cam ramp, where it is in continual contact with both the cam ramp and the pathway, may be slightly different, since the rollers may have different diameters due to manufacturing variations.
Shipping security, skew control, and roller speed capacity have all been improved by the use of clutches with roller control cars. Each roller has an individual control car that surrounds the roller closely enough to retain it securely in the car. Each car, in turn, is retained to the cage by various means that prevent the car from separating from the cage before clutch installation, but which do not interfere with the free travel of the roller after clutch installation. The net result is a secure assembly for shipping and handling purposes, but each roller is still able to freely seek its lockup ready position between the races as the clutch operates. A basically conventional spring is used, which applies its energizing force to the car, instead of directly to the roller. In some designs, the control cars are also guided quite closely by the side rails of the cage as they slide between the side rails during clutch operation. Since the rollers are held square to the cars by the closeness of their fit within the cars, each roller is given a high degree of skew control during clutch operation. Controlling skew helps control spin and uneven loading of the rollers. In addition, various other means can be added to the car to reduce roller spin and wear, such as drag surfaces and rubbing surfaces which interact with the pathway race during clutch overrun. U.S. Pat. No. 4,821,856 to Lederman and U.S. Pat. No. 4,893,702 to Lederman show various embodiments of roller control cars embodying the above features.
The specific designs described above were developed for single row roller clutches. Double row clutches present the unique problem discussed above of potentially differing optimal ready positions within the same roller pair. The close containment that some of the roller control cars described above provide to the rollers would be a drawback if pairs of rollers were simply added to the car without alteration. The smaller roller could potentially be held back from reaching its optimal ready position. This could mean that one roller of the pair, the one held back, would see no load, overloading the other. Furthermore, none of the roller car designs discussed above is specifically designed to apply an energizing force to two rollers at once from a single spring.